This invention relates to capping machines, and more particularly, to a capping head for use in such a machine in the application of pre-threaded caps.
Capping machines for the application of pre-threaded caps to containers have been known for many years. They often have included a chuck which is adapted to rotationally grip a threaded cap to apply a torque thereto for securing the threaded cap on the cooperably-threaded opening of a container, such as a bottle with a threaded finish. The chuck typically is coaxially supported with respect to a rotary spindle by a rotary bearing. Rotary driving torque to drive the chuck may be provided through a magnetic clutch. The chuck thus will rotate the cap into threaded engagement on the container only until further incremental engagement would require greater torque than the magnetic clutch can deliver. At this point, the magnetic clutch begins to slip as the rotary spindle rotates with respect to the chuck. It has been one objective of such arrangement to provide uniform torque for uniform cap application throughout the range of capping operation variables, including capping machine operating speed.
Among the patents on capping machines generally, and specifically turret-type machines, is U.S. Pat. No. 3,771,283. Another patent, British Pat. No. 2,111,964, discloses a capping machine having a limited torque applicator apparatus for applying screw caps to the threaded necks of containers. The requisite torque is transmitted to a cap applicator head from a rotating power shaft by the magnetic attraction between a ring of magnets and a concentrically adjacent ring of magnetizable material.
Practitioners of the art have constantly sought ways to provide more uniform torque for screw cap application than has heretofore been applicable in known magnetic slip clutch arrangements. For example, in many rotary screw capping heads, the inertial mass of the chuck components is of such considerable magnitude as to adversely affect torque transmission to the rotary chuck. This problem has been most common in the higher ranges of capping machine operating speed and has resulted in significant variation of torque as a function of machine operating speed. To overcome this and other causes of nonuniform torque, some capping machines have been provided with sets of different capping heads for different operating speed ranges. While this approach has been helpful, it also has been uneconomical and has unduly complicated variation of capping machine operating speed. This has been especially true of the turret-type machines which have a plurality of identical capping heads that operate in continuous, repeating sequence.
Prior attempts to reduce chuck assembly inertia have included attachment of the clutch magnets by means of adhesive bonding. Another mode of maintaining uniform cap application torque, or more generally, of selectively varying the torque, has been to provide for the selective variation of spacing between the driving and driven elements of the magnetic clutch by the insertion or removal of spacers in the magnetic clutch assembly, or by adjustment of a continuously variable magnet spacing adjustment mechanism. The above-cited British Pat. No. 2,111,964 discloses one such continuously variable spacing adjustment.